1. Field of the Invention
The present invention relates, generally, to vehicle lighting and, more specifically, to a headlamp for a motor vehicle.
2. Description of the Related Art
Conventional light modules and motor vehicle headlamps are known, for example, from DE 10 2012 223 658. The light module described therein has numerous semiconductor light sources, disposed adjacent to one another, for emitting light. A semiconductor light source is designed, for example, as a light emitting diode (e.g. LED chip) having a light emitting surface that is substantially square or rectangular. A primary lens designed as a collecting lens is allocated to each of the semiconductor light sources, which bundles the light emitted from the semiconductor light source allocated thereto. Numerous collecting lenses are disposed adjacent to one another, corresponding to the configuration of the semiconductor light sources, and combined to form a primary lens array. The collecting lenses include, by way of example, a solid transparent material, e.g. glass or plastic. They each have a light entry surface facing the semiconductor light source allocated thereto, and a light exit surface facing away from the semiconductor light source. A bundling of the light emitted from the semiconductor light source occurs by refraction at the light entry surface and/or the light exit surface and/or by total internal reflection at outer border surfaces of the collecting lens. Each collecting lens generates a substantially square or rectangular primary light distribution on its light exit surface thereby, corresponding to the shape of the light emitting surface of the light emitting diode allocated thereto.
The known light module also includes a shared secondary lens designed as a projection lens, for all of the primary lenses. The projection lens is focused on the light exit surfaces of the primary lenses, such that it projects the primary light distributions on the roadway in front of the motor vehicle as corresponding secondary light distributions. The entirety of all of the secondary light distributions corresponds to the resulting overall light distribution generated by the light module, which, for example, is a high-beam light distribution. The projection lens projects the primary light distributions as stripe-shaped secondary light distributions with a significantly greater vertical extension than the horizontal extension. It is conceivable that the individual stripe-shaped secondary light distributions are bordered laterally by sharp vertical light/dark borders. The secondary lens can also be designed as a multi-part lens, such as a double-lens achromatic lens.
A so-called non-blinding high-beam, or a partial high-beam, can be generated with the known light module. Regions are removed from the resulting high-beam light distribution by deactivating individual semiconductor light sources, those regions being where other traffic has been detected. The deactivation of the individual semiconductor light source(s) occurs thereby, dependent on a signal from one or more detectors, which are provided in the motor vehicle for the detection of other traffic in front of the motor vehicle. The detector can include at least one camera, at least one ultrasound sensor and/or at least one radar sensor.
The secondary lens can be designed such that the secondary light distributions projected onto the roadway in front of the motor vehicle border one another directly, without an overlapping of the secondary light distributions. When one of the semiconductor light sources is deactivated, the region in which there is no corresponding secondary light distribution in the resulting light distribution of the light module is bordered by relatively sharp vertical light/dark borders of the illuminated secondary light distribution of the activated adjacent semiconductor light sources. The large gradient in the illumination can be subjectively experienced by a driver of the motor vehicle as having a disruptive effect.
Alternatively, in DE 10 2012 223 658 it is described that the secondary lens is designed such that the secondary light distributions projected therefrom onto the roadway in front of the motor vehicle are disposed adjacent to one another, wherein at least the lateral regions of adjacent secondary light distributions overlap one another. This can be obtained in that a fundamental shape of a light exit surface on the projection lens is modulated such that a single primary light distribution is converted to a plurality of corresponding sub-regions of the corresponding secondary light distribution, wherein the sub-regions are of equal size, and are displaced with the same orientation in the horizontal direction in relation to one another, and disposed such that they overlap one another. The entirety of all sub-regions arising from a specific primary light distribution forms the corresponding secondary light distribution. Therefore, sharp vertical light/dark borders, which border the stripe-shaped secondary light distributions, and thus the large gradients in the illumination formed when a semiconductor light source is deactivated, are avoided.
Collecting lens arrays are best suited for use as primary lenses, because they make limited demands on raw materials, mold precisions and positioning precisions. When collecting lens arrays are used, comparatively small secondary lenses are sufficient. As a result, the aberrations in the secondary lens can also be kept small. The prerequisite for this, however, is a relatively large aperture (the relationship of the focal length to the diameter of the effective entry surface of the secondary lens). With lens systems, the aberrations are primarily color errors, whereas with reflection systems with small apertures, these are primarily comatic aberrations.
One disadvantage of the primary lenses designed as a collecting lens array is that an aperture angle of the emitted light bundle in relation to an optical axis of the secondary lens is basically the same size in all directions, and thus can only be varied to a small degree. Expressed differently, this means that an enlargement of the light emitting surface of the semiconductor light sources with a lens disposed directly in front of the light source is of a similar size, both horizontally as well as vertically. An anamorphic enlargement of the primary light distributions can only be obtained within very narrow limits. Because the vertical expansion of stripe-shaped matrix light distributions is a multiple of the width thereof, however, it would be desirable for the enlargement of the light emitting surfaces of the semiconductor light sources to be adjusted to the stripe-shaped secondary light distributions, thus to increase the size of the illuminated surfaces on the light exit surfaces of the primary lens more in the vertical direction than in the horizontal.
As set forth in the Helmholtz-Lagrange invariant, one can significantly reduce the angle of emission for the primary lens in the vertical cross-section with this measure, by which the vertical expansion, i.e. the height, of the secondary lens, can be reduced in the opposite manner:y×n×σ=y′×n′×σ′
Where y, and y′ are the object or image size; σ, and σ′ are the object or image-side aperture angle; and n, and n′ are the object or image-side refraction index.
Furthermore, with the known matrix high-beam light modules, due to the large focal lengths of the secondary lenses, there are problems with the structural lengths of the light modules. The long focal lengths arise thereby due to the required width/spacing of the generated matrix light distributions, on one hand, and the spacing of the semiconductor light sources/primary lens on the other hand. The width of the light distributions is largely dependent on the desired resolution and performance of the light module, while the spacing of the primary lenses is primarily dependent on the required minimum spacing and component sizes of the semiconductor light sources.
For this reason, it has already been considered in the prior art to bend the beam path by a deflecting mirror or a deflecting prism, thus reducing the critical structural lengths of the light module. Deflection mirrors or prisms cause, however, additional losses of luminous flux in the beam path.